Artifacts in rendered geometry which appears okay in openGL / Solid view?
Your real problem appears to be scale:

I think caused by clipping plane being way beyond what is necessary.

You had it set to 1mm - 1km
Overlapping faces
My first impression is that you are trying to fix the wrong problem. I suspect that the reason you are using BSurfaces is because you don't know why you are getting scratches. The scratches is a much more interesting problem, and knowing how to fix those will help you in future modelling.
If I am correct, the 'scratches' as you call them, are the result of overlapping geometry, and this results in z-fighting. The scale you are modelling at compared to the viewing world scale will result big enough rounding errors to make this noticeable.